1. Field of the Invention
The present invention relates to methods for fabricating periodic structures.
2. Description of the Related Art
Photonic crystals having a periodic change in the refractive index with a periodicity being comparable to the light wavelength will be described. In semiconductors, a photonic band-gap (band-gap for light) is formed by a Bragg reflection of light waves by a periodic distribution of refractive index, similar to a band gap formed by a Bragg reflection of electron waves by periodic potential of atomic cores.
Some structures exhibiting such a photonic band-gap have been reported. In U.S. Pat. No. 5,335,240 (referred to as Patent Document 1, hereinafter), a woodpile structure which is one of three-dimensional periodic structures is proposed. This structure can exhibit a photonic band-gap (complete photonic band-gap) for incident light from all directions. The woodpile structure can perform various effects, such as controlling of spontaneous emission light, by exhibiting the complete photonic band-gap, and a functional element which is nonconventional can be achieved. For example, the appearance of a localization mode in a band can be achieved by introducing a defect structure formed by disarraying a part of the three-dimensional periodic structure; thus, a resonator which confines only light having a prescribed wavelength can be achieved. In order to achieve such a functional element, the appearance of a complete photonic band-gap having a broader wavelength band is further required.